Design of an LLC Resonant Converter for Driving Multiple LED Lights Using Current Balancing of Capacitor and Transformer

Transcription

1 Enegies 05, 8, 5-44; doi:0.3390/en8035 Aticle OPEN AESS enegies ISSN Design of an LL Resonant onvete fo Diving Multiple LED Lights Using uent Balancing of apacito and Tansfome Jae-Hyun Han and Young-heol Lim, * LG Innotek o., Ltd., 6, Hanamsandan 5beon-o, Gwangsan-gu, Gwangju , Koea; jhhanb@nave.com Depatment of Electical Engineeing, honnam National Univesity, Gwangju , Koea * Autho to whom coespondence should be addessed; yclim@chonnam.ac.k; Tel.: ; Fax: Academic Edito: his Bingham Received: 3 Novembe 04 / Accepted: Mach 05 / Published: 8 Mach 05 Abstact: In this study, to achieve the constant cuent dive and bightness contol without a sepaate pulse width modulation (PWM) convete, a single convete is designed and veified by expeiment unde the condition of a multiple LED light load with diffeent output voltage (Vf) chaacteistics. In the case of the input of 40 Watt class level, the poposed convete can dive two voltage type 95 Vdc (300 ma) light emitting diode (LED) lights loads and 0 Vdc (300 ma) LED lights loads simultaneously. In addition, to impove commecial compatibility, the poposed convete is opeated in a wide ange of the input voltage 90~64 Vac; also, the Powe Facto oection (PF) cicuit with the input powe facto of moe than 0.9 is added. In ode to maximize the powe convesion efficiency, a LL esonant convete is applied to the PF block with the output voltage of 380 Vdc and to a D-D convesion block. Finally, eliability of the poposed convete is veified though total hamonic distotion (THD) and electomagnetic intefeence (EMI) tests. Keywods: multiple LED lights; LL esonant convete; cuent balancing; efficiency; powe facto; total hamonic distotion (THD); electomagnetic intefeence (EMI) test; life time

2 Enegies 05, 8 6. Intoduction Recently, the topic of low-cabon geen gowth industy has been actively eseached and developed. Especially, the enewable enegy and cabon dioxide emission maket has been apidly expanding due to climate change and the enegy cisis. Enegy savings ae equied in ode to educe the cabon dioxide that causes the geen-house effect. The total global powe consumption of lighting is tillion, 00 billion kwh, which is %~5% of the global annual powe consumption..7 billion tons of cabon oxide is emitted annually accoding to the powe consumption of lighting. Fo this eason, eseach into highly efficient lights has been actively caied out. A Light Emitting Diode (LED) has high luminous efficiency and 0%~30% powe savings compaed to a conventional light souce. Annually 50 billion kwh powe and 50 million tons of cabon oxide could be educed though the use of LED lights [,]. The LED is tuned on when the applied voltage is moe than the fowad voltage, a LED is a diode. To modify the vaiable lighting chaacteistics, multi LEDs can be composed as a seies aay o paallel sting. Fo the design of an LED convete, consideation of LED fowad voltage vaiation (±5%~0%) is equied [3 8]. Figue shows a simplified LED diving cicuit with a multi-sting stuctue. Since the cuents diffe between each channel accoding to the impedance, a lage cuent can be injected into one channel of low impedance and can educe the life time of the LEDs, leading to thei destuction [9,0]. Recently, to achieve LEDs with high luminous efficiency, multi LEDs ae used in a single luminay stuctue. In the case of multi-sting lighting, each LED sting has a diffeent impedance. Because all the LEDs (Vf) have diffeent voltages, an individual boost o buck PWM convete is needed fo each LED. In addition, in the case of outdoo lights such as steet lights and secuity lights, vaiable bightness is needed accoding to the lighting conditions and a multi LED dive is equied [ 3]. Howeve, when applying individual convetes to each LED, the system cost is inceased and the efficiency and life time of the system ae educed. Figue. Simplified LED diving cicuit with multi-sting stuctue. In this pape, an LL esonant convete fo diving multiple LED lights using the cuent balancing of a capacito and tansfome is poposed. The poposed convete can dive multi LED stings without an individual convete with constant cuent contol and dimming contol. To impove the compatibility

3 Enegies 05, 8 7 of the poduct, the poposed convete is designed with a wide input voltage ange of 90~64 Vac and high powe facto (ove 0.9). Futhemoe, to maximize the efficiency, a D/D block is designed as an LL convete. A THD and an EMI noise tests ae pefomed to veify the eliability of the poposed convete.. onvete fo Diving LED Lights.. onventional onvete fo LED Application Figue shows a conventional convete type fo high powe LED lighting powe. The system consists of an A powe input pat and a PF cicuit fo impoving the powe facto, a D/D convete fo building output voltage, and an LED dive fo poviding a constant cuent to the LED load. A fly-back and LL esonance convete ae usually used fo the D/D convete [4 7]. Figue. onventional LED diving cicuit. Figue 3a shows a buck D/D convete mostly used fo constant LED cuent contol. The buck convete can be adapted in the case of an LED voltage lowe than the input voltage, and equies a duty atio of less than 85%. The output voltage is contolled by the MOSFET s on/off opeation though the chage and dischage of an inducto cuent. Figue 3b shows a boost D/D convete which is used when the LED voltage is highe than the input voltage. The convete can achieve 90% uppe efficiency and has an advantage in EMI due to the filte effect of the main inductance [8]. (a) (b) Figue 3. Buck and Boost convete fo LED Application. (a) buck convete; (b) boost convete.

4 Enegies 05, Poposed uent Balancing onvete fo Diving LED Lights Usually, a high switching fequency is equied to educe the size of the convete, but this causes an incease of switching loss in a had switching mode. In this pape, an LL esonance convete with Zeo Voltage Switching (ZVS) opeation is poposed. The poposed convete using high fequency and ZVS is adapted to educe switching loss. Figue 4 shows the schematic of the poposed convete. As shown, a D blocking capacito, clamping diode, and cuent balancing tansfome ae used instead of the switching egulato in the second stage of the convete. I S Da T D a a Dn T D n n oss L ITa ITa I Tn I Tn I P V S oss L m a a n n I m R S LED a LED LED n a LED n Figue 4. Poposed cuent balancing convete. Poposed multi LED lights dive convete consists of fou blocks. BLK: A PF block fo achieving high powe facto with wide input voltage ange fom 90 Vac to 64 Vac. BLK: A half bidge block makes a squae wave voltage with 380 Vdc input and nealy 50% duty atio. The block has a shot dead time to ensue continuous cuent flow. BLK3: A esonant tank block consisting of a capacito and magnetizing inductance of tansfome L m. The esonance tank opeates with high fequency and ceates a sinusoidal cuent fom the squae wave voltage fom BLK. Since the pimay cuent I P is delayed by esonance, MOSFET is tuned on with the ZVS condition. BLK4: A esisto R S of this block is used fo LED cuent sensing and limiting. A egulated D voltage is applied to an LED load though D a ( D n ) and D a ( D n ). a ( n ) and a ( n ) ae connected paallel to the LED load and the D voltage is made smooth. The lage capacitance can futhe educe A noise. A capacito B allows only an A signal to pass. At the fist half cycle of A signal, the capacito B compensates the voltage diffeences of each channel and dives a high voltage channel. At the othe

5 Enegies 05, 8 9 half cycle of the A signal, the capacito B emoves the offset voltage and dives a low voltage channel. Thus, duing a single peiod ( T S ), the capacito chages/dischages the total enegy and the change of voltage is zeo. This can be expessed by Equation (). Based on Equations () and (), the voltage change of the capacito B is calculated as zeo, which is a basic pinciple of a capacito volt-sec balance equation: tt s VB ( tts ) VB( t) i t Bdt () tt s 0 ib ( t) dt T t () s Since the balancing tansfomes ae opeating unde A excitation, the following Equation (3): NTa ita NTa ita N Tn i Tn N Tn i Tn (3) Pimay tuns and pimay cuent espectively of the balancing tansfome. N TnK and i TnK denote the seconday tuns and seconday cuent espectively of the Kth balancing tansfome. Since with the loop connection the seconday winding cuent is equalized as follows: ita ita itnk (4) And this futhe esults in: ita ( NTa / NTa ) ita (5) In this pape cuent balancing tansfome T a ( T n ) fo constant cuent contol has a : winding atio accoding to equation NTa ita NTa ita and the same cuent flows at LED a ( LED n ) and LED a ( LED n ). The cuent which flows though tansfome Ta can be expessed by Equation (6): ita ita iled (6) The voltage acoss the second side of tansfome Tcan be expessed by Equation (7): Vs ( vb vda vtavledavrs ) vb vda vta vleda (7) Figue 5 shows the cuent and voltage wavefoms accoding to the opeation mode of the LL esonant convete. Mode ( t 0 to t ): At t 0, Q is on state and Q is off state. The switch cuent I P flows though the body diode of MOSFET Q by, and the L esonance and a voltage acoss the MOSFET Q is zeo. A voltage of oss which is connected to the MOSFET Q dain-souce is chaged to the Vin level. An output cuent then stats to flow though diode D a (Figue 6).

6 Enegies 05, 8 30 Q Q Figue 5. Opeation wavefom of LL esonant convete. D a D a oss L oss L m LED a a a LED a R S Figue 6. icuit diagam duing Mode. Mode ( t to t ): A Q is in the tun-on state and inducto cuent I P flows in the positive diection. An input voltage is applied to a tansfome and cuent ( I m ) of the magnetizing inductance ( L m ) inceases linealy (Figue 7).

7 Enegies 05, 8 3 D a D a oss L oss L m LED a a a LED a R S Figue 7. icuit diagam duing Mode. Mode 3 ( t to t 3 ): At the t, Q is in the tun-on state and Q is in the tun-off state. Inducto cuents I P and I have the same value and the output cuent is zeo. The cuent I begins to chage m m oss of Q. At the same time, oss of Q dischages by I m. haged capacitos that ae connected paallel to each LED supply the enegy to the LED loads (Figue 8). D a D a oss L oss L m LED a a a LED a R S Figue 8. icuit diagam duing Mode 3. Mode 4 ( t 3 to t 4 ): Q is in the tun-off state and Q is in the tun-on state. The cuent I P flows though the Q body diode and the voltage acoss the Q becomes zeo (ZVS ondition). An output cuent flows to the LED load though capacito B and diode D a. D a is in evese bias with no cuent flowing though (Figue 9). Mode 5 ( t 4 to t 5 ): An opposite mode to Mode. In this mode, a half A voltage accoding to the cente tap of the tansfome is applied to an LED though D a (Figue 0).

8 Enegies 05, 8 3 D a D a oss L LED a oss L m a a LED a R S Figue 9. icuit diagam duing Mode 4. Da D a oss L oss L m LED a a a LED a R S Figue 0. icuit diagam duing Mode 5. Mode 6 ( t 5 to t 6 ): An opposite mode to Mode 3. In this mode, a half A voltage fom the cente tap of the tansfome is applied to an LED though D a (Figue ). Da D a oss L oss L m LED a a a LED a Figue. icuit diagam duing Mode 6.

9 Enegies 05, 8 33 Figue shows an equivalent cicuit fo the pimay side of the LL esonant convete. A squae wave geneato block and esonant tank block ae in this cicuit. L I o L m Figue. Equivalent cicuit of pimay side convete. Resonant fequency and tansfome tun atio can be expessed by Equations (8) and (9): f 0 L (8) π V in / n V (9) An LL convete can be descibed using fundamental appoximation. Figue 3 shows a fundamentally appoximated cicuit accoding to the ac input fo the pimay side of the LL esonant convete. Load voltage V oa, load cuent I oa, and load esistance R oa can be expessed by Equations (0) (). Equation (3) expesses the gain chaacteistics and Equations (4) and (5) expess the Quality Facto. 0 L I P I m L m R oa I oa V oa Figue 3. Fundamental appoximated cicuit of pimay side. Voa nv0 (0) π Ioa Io / n ()

10 Enegies 05, nRL Roa () π jωl R m oa nvo jωlm Roa Ln fa jωlmroa in jωl n n n a a jωlm Roa jω Av V / L f ( f )( jf L Q) min m, a, a oa o (3) L / f L Q f L (4) R f L f min π ( L L ) m Figue 4 shows the opeation classification of the LL convete. The opeation of an LL convete can be classified into 3 egions accoding to switching fequency. In the case wheeby the phase of input voltage (Vac) pecedes the phase of I P, it can be expessed as the zeo cuent switching (ZS) opeation egion. Inductive Region (ZS) apacitive Region (ZVS) Unity gain Region (5) V L V V V L L V V Figue 4. Opeating egion of LL esonant convete. Figue 5 shows the gain chaacteistics of an LL esonant convete in the condition of Ln( Lm / L). The opeation mode is classified as within the ZVS egion with high switching fequency and the ZS egion, with low switching fequency elative to esonant fequency. An LL convete is usually used with a ZVS condition because in the case of a ZS condition, a high cuent is injected when the switch is on, which destoys the MOSFET. If the maximum gain point is equied to move left o a balanced gain chaacteistic is equied, enlaging L n can be useful. Figue 6 shows the Mode opeation in the equivalent cicuit of the convete s seconday side. A pimay side tansfome is conveted to inductance in the equivalent cicuit. L m is mutual inductance, while L lk and L lk ae the leakage inductance of tansfome at the pimay and seconday side, espectively. R L and R L ae conveted values of the LED load. The input voltage is twice the cente tap voltage Vin /4n, thus R L is moe appopiate fo a high voltage LED load than R L. An output cuent flows though B by D a and L b. A chaged enegy in the a dischages to R L.

11 Enegies 05, 8 35 Figue 5. Gain chaacteistics of LL esonant convete. Figue 6. Equivalent cicuit of seconday side convete (Sinωt > 0). Figue 7 shows the Mode 5 opeation. The input voltage is twice cente tap voltage Vin /4n, thus R L is moe appopiate fo use with a high voltage LED load than R L. Figue 7. Equivalent cicuit of seconday side convete (Sinωt < 0). Figue 8 shows the simply modified equivalent cicuit of Figue 7. The load voltage is V o / and the load cuent is I o, and the LED load can then be expessed by R /4 L.

12 Enegies 05, 8 36 Figue 8. Simplified equivalent cicuit of seconday side convete. Figue 9 shows a simplified equivalent cicuit compaed to that of Figue 8, elative to voltage gain. Figue 9. Simplified equivalent cicuit of seconday side convete. The voltage gain in a negative egion can be expessed by Equation (6) and the voltage gain accoding to switching fequency can be found by this equation. Equation (7) shows the voltage gain in a positive egion: RL Vo Lm 4n 4 V in Lm Llk L Lb n (6) RL ω n ωb 4 RL Vo Lm n 4 V in Lm Llk L Lb n (7) RL ω n ωb The tansfome equies design accoding to the high voltage load and the tun atio is detemined using Equation (8): NP VS 380V n.5 N ( V V ) (0V. V) (8) S LED Da An equivalent esistive value of the LED load is expessed by Equation (9): 8n Vo Req 03 (9) π P o

13 Enegies 05, 8 37 The esonant component can be detemined fom Equation (0). An equation of Q facto is ( L / ) / R eq and 0.4~0.5 is the ideal value. The Q facto of the poposed convete is detemined to be 0.45 and the esonant fequency is detemined to be 85 khz. Fo the expeiments, two 0 nf capacitos ae adapted with paallel connection: ( Q0.45, fo 85 khz) 0nF 3 πq f R o eq The esonant component L can be detemined fom Equation () and 0 μh is selected in the poposed convete accoding to the tansfome bobbin and winding limitation: L (3.485 ) 0nF (π fo) khz 75μH The pimay side inductance L P is expessed in Equation (). The L k is a ation of the mutual inductance to the pimay side leakage inductance. Usually, 3 to 8 is used fo the L k value and 6 is selected fo the poposed convete. The L P is calculated as 659 μh fom Equation () and 650 μh is applied fo the expeiments: 3. Expeimental Results ( k ) (6) (k ) (6 ) 6 LP L (750 ) 659μH Table shows the system specification of the poposed convete. Table. System specification of the poposed convete. omponent Pat Desciption Dive I PF LL MOSFET Q, Q Tansfome apacito Diode a T T a SY990 (Onsemi) L6599 (STmico) STF3NM60 (STmico) 600 V/3 A EP384 (ova Hiteck) 5T:35T:35T (650 μh:350 μh:350 μh) L = 0 μh EE00 (ova Hiteck) 00T:00T (3 mh:3 mh) (0) () ( Lk Lm / Llk) () Flim-ap 0 nf/630 V (Pilko) EA (0 nf) B Flim-ap nf/630 V (Pilko) a, a eamic-ap μf/00 V (Muata) EA seial ( μf) D, D a STTH8T06 (STmico) 600 V/8 A Table shows a compaison of the pesented convete and a conventional convete. As shown, the poposed convete can educe the quantity of the I, MOSFET, aluminum capacito, and diode, etc. fo each channel. Figue 0 is a photogaph of the poposed convete.

14 Enegies 05, 8 38 Table. ompaison between the poposed convete and a conventional convete. omponent Pat onventional onvete Poposed onvete I PF, LL EA EA Buck 4 EA 0 EA MOSFET Q, Q EA EA Buck 4 EA 0 EA Tansfome T EA EA T a 0 EA EA Inducto Buck 4 EA 0 EA apacito, B EA (B 0 EA) EA E-ap 5 EA 0 EA LL EA 0 EA Diode Buck 4 EA 0 EA Poposed 0 EA 4 EA Total 9 EA 3 EA Figue 0. Photogaph of the poposed convete. The expeiments ae pefomed with the poposed convete, which is designed fo a 40 Watt multi-led dive. Two 95 Vdc (300 mams) LED loads and two 0 Vdc (300 mams) LED loads ae applied fo multi LED loads. Figue shows the test wavefoms of the LL convete unde full load condition. hannel is the wavefom of the tansfome s pimay side voltage ( V L m ), hannel is the wavefom of the tansfome s pimay side cuent ( I P ), and channel 3 is the wavefom of the tansfome s seconday side cuent. In the case of channel 3, a 90 degee phase diffeence occus accoding to the winding diection, and the cuent path is detemined accoding to the voltage diffeence among each channel.

15 Enegies 05, 8 39 IS VLm I P Figue. Test wavefoms of LL convete unde the full load condition. Figue shows the LED voltage and cuent in the cases whee the convete is tuned on and off. The poposed convete pefoms stable tun on and soft tun off without an abnomal spike o malfunction. (a) (b) Figue. LED voltage and cuent in the case whee the convete is tuned on and off. (a) Tun on; (b) Tun off. Figue 3 shows the output voltage-cuent wavefom at unde 00% and 0% bightness condition. As shown, a constant cuent contol is pefomed accoding to dimming contol.

16 Enegies 05, 8 40 Figue 3. Output voltage-cuent wavefom unde 00% and 0% bightness condition; (a) h~h4 output voltage-cuent wavefom unde 00% bightness condition; (b) h~h4 output voltage-cuent wavefom unde 0% bightness condition. Figue 4 shows the electical chaacteistics of the poposed convete at 0 Vac condition. At the 36.9 Watt input powe, efficiency is calculated to be 93% with fou channel LED loads (94.5 V 0.30 A + 8 V 30 A V A + 7. V 0.30 A = 7.55 Watt). The powe facto (λ) is In the case of THD, the atio of cuent is limited with the hamonic ode. Accoding to K standads (K ) [3], a thid hamonic cuent equies less than PF 30% and a fifth hamonic cuent equies less than PF 0% of fundamental wave. As shown at Figue 4, the total hamonic distotion of input cuent ( I THD) is 5.64%, the atio between the thid hamonic cuent and the fundamental cuent (I()) is 3.84% ( A/0.63 A 00%),

17 Enegies 05, 8 4 and the atio between the thid hamonic cuent and the fundamental cuent (I()) is 6.58% (0.046 A/0.63 A 00%), thus the poposed convete satisfies the K standad (K ). Figue 4. Electical chaacteistics of the poposed convete. Figue 5 shows the EMI test esult of the poposed convete. Figue 5a shows the Radiation Emission (RE) esult. The maximum noise value is.3 dbμv/m at MHz, and at this point, has a 7.7 db magin accoding to the standad ISPR 5 lass B. Figue 5b shows the onduction Emission (E) esult. The minimum magin value is 8.34 db at 37 khz accoding to ISPR 5 lass B. (a) Figue 5. ont.

18 Enegies 05, onclusions (b) Figue 5. EMI test esults. (a) EMI RE Test esult; (b) EMI E Test esult. LEDs have high luminous efficiency and 0%~30% saving cost effect compaed to a conventional light souce. Theefoe, eseach and development on an LED dive has ecently been actively caied out. Geneally, LED s can be configued with a vaiety of opeating voltages and cuents. Also, LED s have the advantage of being able to have a multi-sting channel. A conventional multi LED dive system uses an individual LED dive fo each channel and this induces the need fo many components, educes the system life time, and has low efficiency. In this pape, a novel method fo a multiple LED dive convete using capacito and tansfome cuent balancing is poposed. The poposed convete has consideably fewe components and thus saves space compaed to the conventional convete. The poposed convete consists of fou blocks: () the PF block fo high powe facto implementation; () a half bidge block to geneate a squae wave voltage with 380 Vdc input; (3) and (4) both blocks consist of a esonant tank and balanced capacito-tansfome cicuit. The poposed convete opeates using ZVS commutation to achieve high efficiency and to impove the EMI. Though the theoetical analysis and expeiments, the poposed convete is analyzed and veified. In the expeimental esults, the poposed convete was measued at a high powe facto (ove 0.9) and high efficiency (ove 90%) pefomance. In addition, the EMI and THD chaacteistics wee veified fo the eliability of the convete.

19 Enegies 05, 8 43 Autho ontibutions Jae-Hyun Han collected expeimental data and pepaed figues, Young-heol Lim and Jae-Hyun Han wote and eviewed the manuscipt. Nomenclatue f, o f min esonant fequency and minimum esonant fequency L, L pimay and seconday side inductance of the balanced tansfome T a b b L lk leakage inductance of pimay side T L m magnetization inductance of tansfome T L p pimay side inductance of tansfome T L, inductance and capacitance of esonant tank Av tansfe gain of equivalent tank cicuit n tansfome tun atio NP, N S numbe of tuns in the pimay and seconday coils espectively Q quality facto of equivalent tank cicuit R eq R L an equivalent esistive value of the LED load esistance of equivalent cicuit RL, R L an equivalent esistive value of the LED a and LED a VB, I B voltage and cuent of capacito B vda, v Da voltage of diode D a, D a vleda, v LEDa voltage of LED a, LED a Vo, Io, P o output voltage and cuent and powe of equivalent cicuit Voa, Ioa, R oa load voltage and cuent and esistance of equivalent cicuit (fundamental appoximation) V S voltage acoss the seconday side of tansfome T v, v pimay and seconday side voltage of tansfome T a Ta Ta onflicts of Inteest The authos declae no conflict of inteest. Refeences. Tan, Y.K.; Huynh, T.P.; Wang, Z. Smat pesonal senso netwok contol fo enegy saving in D gid poweed LED lighting system. IEEE Tans. Smat Gid 03, 4, Lv, X.; Loo, K.H.; Lai, Y.M.; Tse,.K. Enegy-saving dive design fo full-colo lage-aea LED display panel systems. IEEE Tans. Ind. Electon. 04, 6, Hui, S.Y.R.; hen, H.; Tao, X. An extended photoelectothemal theoy fo LED systems: A tutoial fom device chaacteistic to system design fo geneal lighting. IEEE Tans. Powe Electon. 0, 7, Zhang, J.; Xu, L.; Wu, X.; Qian, Z. A pecise passive cuent balancing method fo multioutput LED dives. IEEE Tans. Powe Electon. 0, 6,

20 Enegies 05, Zhao,.; Xie, X.; Liu, S. Multioutput LED dives with pecise passive cuent balancing. IEEE Tans. Powe Electon. 03, 8, Lin, R.L.; hang, Y..; Lee,.. Optimal design of LED aay fo single-loop M buck-boost LED dive. IEEE Tans. Ind. Appl. 03, 49, Kim, M.G. Eo amplifie design of Peak uent ontolled (P) buck LED dive. IEEE Tans. Powe Electon. 04, 9, Zhang, F.; Ni, J.; Yu, Y. High powe facto A-D LED dive with film capacitos. IEEE Tans. Powe Electon. 03, 8, Lee, A.T.L.; Sin, J.K.O.; han, P..H. Scalability of quasi-hysteetic fsm-based digitally contolled single-inducto dual-sting buck LED dive to multiple stings. IEEE Tans. Powe Electon. 04, 9, Zhang, R.; hung, H.S.H. Tansfome-isolated esonant dive fo paallel stings with obust balancing and stabilization of individual LED cuent. IEEE Tans. Powe Electon. 04, 9, Hasan, J.; Ang, S.S. A high-efficiency digitally contolled RGB dive fo LED pixels. IEEE Tans. Ind. Appl. 0, 47, Lo, Y.K.; Wu, K.H.; Pai, K.J.; hiu, H.J. Design and implementation of RGB LED dives fo LD backlight modules. IEEE Tans. Ind. Electon. 009, 56, Ng, S.K.; Loo, K.H.; Lai, Y.M.; Tse,.K. olo contol system fo RGB LED with application to light souces suffeing fom polonged aging. IEEE Tans. Ind. Electon. 04, 6, Feng, W.; Lee, F..; Mattavelli, P. Optimal tajectoy contol of LL esonant convetes fo LED PWM dimming. IEEE Tans. Powe Electon. 04, 9, Hong, S.W.; Kim, H.J.; Pak, J.S.; Gun, Y. Seconday-side LL esonant contolle I with dynamic PWM dimming and dual-slope clock geneato fo LED backlight units. IEEE Tans. Powe Electon. 0, 6, heng,.a.; heng, H.L.; hung, T.Y. A novel single-stage high-powe-facto LED steet-lighting dive with coupled inductos. IEEE Tans. Ind. Appl. 04, 50, Wu, X.; Zhang, J.; Qian, Z. A simple two-channel LED dive with automatic pecise cuent shaing. IEEE Tans. Ind. Electon. 0, 58, Kim, J.K.; Lee, J.B.; Moon, G.W. Isolated switch-mode cuent egulato with integated two boost LED dives. IEEE Tans. Ind. Electon. 04, 6, by the authos; licensee MDPI, Basel, Switzeland. This aticle is an open access aticle distibuted unde the tems and conditions of the eative ommons Attibution license (